Hi,
As Robert mentioned, the oral glucose tolerance test is the main test used to establish glucose intolerance and CFRD (CF related diabetes). As a CF person gets older, the risk of developing CFRD increases. I don't have exact numbers, but it's important to follow the CFF's recs of every year glucose tolerance tests as MANY CF pts get missed just on random glucose checks (either inpatient labs or outpatient labs) and even the hemoglobin A1C test may be normal despite being with CFRD.
A lot of CF people have red blood cells that turn over faster than normal. Red cells that live 3 months, and are exposed to higher glucose levels, will "hook" onto "glucose product" and thus, once the hemoglobin A1C test is drawn, it will be higher. However, in a lot of CF people cases, the red cells die earlier than normal, thus, not having enough time to sit there and "hook" onto the "glucose product." Therefore, if the hemoglobin A1C is normal, that DOESN'T eliminate the risk of CFRD.
People can have glucose intolerance for years in which drinking the 70 grams of carbs will show a high glucose 1 hour after that drink, but will have a normal glucose level 2 hours post drink. It's something that CF MDs keep in mind as the CF pt advances in age and during health exacerbations. During a physical stress, a CF pt may need some insulin, but when healthy, the CF pt most likely won't need insulin.
At some point, due to CF progression with lung issues as well as just the normal "cystic" scarring of the pancreas, the pancreas can not produce enough insulin (and the cells of the body can't utilize insulin also). That's when you can convert over to CFRD status. You can only require intermittent insulin until the body's need for insulin outweighs what the pancreas produces. Once that happens, insulin use is pretty much required daily.
I have had glucose intolerance for several years, never really thinking much of it. I used insulin once a few years ago during a significant CF exacerbation. However, for the most part, my glucose levels have been pretty normal.
Now, last week I just had the oral glucose tolerance test. My fasting level was 112 (no food for 8 hours prior to lab draw), 1 hour was 270's and 2 hour was 230's. According to the CF standards, all my values were abnormal. My CF dr labeled me as a CFRD patient now and will now have to focus on insulin therapy (when my glucoses are above a certain point) and will have to test at least 4 times a day with the meter.
Now remember, the diagnosis of CFRD does not mean you will or EVER should follow the standard care plan for an insulin dependent diabetic person. CF people should NOT restrict their calorie intake at all. You monitor sugar levels and adjust insulin requirements to meet your intake. The goal of insulin is to allow you to eat as much as you can (as a majority of CF people need to maintain a high caloric intake) and utilize the glucose effectively. So if non CF MD people start telling you to go on a strict caloric diet and only consume XX carbs per meal, contact your CF dr -- that info is not for CF people who develop diabetes.
I am so sorry this is so long. I work as a Peds NP in an ICU and find this a very interesting subject to discuss (not to mention that I now am dealing with it myself!).
Contact me if you have any questions.
Thanks, Jenn
30 year old with cf and new onset CFRD
